This application claims the priority of Japanese Patent Application No. 4-199171 filed on Jul. 2, 1992 which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an overload protection apparatus for a small-sized tripod head and, more particularly, to the structure of a measure for protecting the driving portion of a tripod head which directs a camera or the like to a desired direction by remote control, when overload is applied to the driving portion.
2. Description of the Related Art
In photographing by a television camera in broadcasting of ITV (Industrial Television), CCTV (Closed-Circuit Television) or the like, the television camera is often remote-controlled in order to take a good picture of a subject or to take a picture in a predetermined range. As a means for turning the television camera, a tripod head is used.
FIG. 7 shows the structure of a conventional tripod head apparatus used by ITV. Two driving shafts 2 and 3 are provided to the tripod head apparatus in such a manner that they project from the side of a box body 1 produced by die casting or the like, and are orthogonal to each other at the right angle within the box body 1. Supporting disks 4 and 5 are attached to the projecting portions of these supporting shafts 2 and 3 through springs 6 and 7. A television camera is fitted to either of the supporting disks 4 or 5, and the other one is attached to a supporting wall (or a supporting stand) or the like. A motor driving portion (not shown) is connected to the other ends of the supporting disks 4 and 5, thereby rotating the driving shafts 2 and 3. For example, when the supporting disk 4 is attached to the supporting wall and a television camera is fitted to the supporting disk 5 by a special blacket so as to be in parallel with the front surface of the box body 1, the television camera is tilted (vertical direction) by the rotation of the supporting shaft 2, and panned (horizontal direction) by the rotation of the supporting shaft 3. In this way, it is possible to obtain a picture in a desired range by remote control.
In such a tripod head apparatus, a slip mechanism is used in order to protect the driving portion from overload. That is, as shown in FIG. 8, the supporting disk 4 (5) is connected to the driving shaft 2 (3) by using a fixing screw 8 in such a manner that the driving shaft 2 (3) can rotate within the box body 1, and the spring 6 (7) is fitted between a flange 9 and the supporting disk 4 (5) which are integrally attached to the driving shaft 2 (3). As a result, while the driving shaft 2 (3) and the supporting disk 4 (5) are connected to each other by the frictional force based on the urging force of the spring 6 (7), when overload is applied, the spring 6 (7) and the supporting disk 4 (5) slip, thereby reducing the load on the motor, the gears, or the like.
In the slip mechanism of the tripod head apparatus, however, since it is difficult to adjust and control the friction torque which is set by the springs 6 and 7, and the motor idles even when overload is applied thereto, electric power is wasted and the life of the motor is shortened.
The box body 1 of the tripod head apparatus is relatively large (the length and breadth are about 10 and several cm) and heavy. In response to the recent development of smaller-sized, lighter-weighted and simplified television cameras, the present applicant has proposed a smaller-sized tripod head apparatus. In this case, however, use of the slip mechanism is an obstacle to the reduction in the size and the weight of the tripod head apparatus.